The present invention relates to a photoelectric conversion element and a method for manufacturing the photoelectric conversion element. The present invention relates more specifically to an easy-to-manufacture organic-inorganic hybrid photoelectric conversion element having high photoelectric conversion efficiency and excellent durability.
Photoelectric conversion elements have been used for various optical sensors, copiers, solar cells, etc. The solar cells, in particular, are representative examples which utilize renewable energy and are becoming widely available. Examples of the available solar cells include a silicon-based solar cell, a CIGS-based solar cell, and a CdTe-based solar cell.
Meanwhile, studies are being conducted in which an organic material is applied to a photoelectric conversion material as an alternative for an inorganic material used in the above solar cells. Development of an organic thin-film solar cell and a dye-sensitized solar cell is in progress. Such solar cells can be manufactured using a coating process without a vacuum process. This may markedly reduce manufacturing cost. Thus, such solar cells should be a next-generation solar cell.
Unfortunately, the current organic thin-film solar cell and dye-sensitized solar cell have insufficient photoelectric conversion efficiency and low durability when compared with the above solar cells using an inorganic material.
Recently, a solar cell has been disclosed that uses, as a photoelectric conversion material, a lead complex with a perovskite crystal structure and an electrolytic solution (Non-Patent Document 1).
Further, the electrolytic solution used in the solar cell disclosed in Non-Patent Document 1 has been replaced by 2,2′,7,7′-tetrakis(N,N-dimethoxyphenylamine)-9,9′-spirobifluorene (hereinafter, referred to as “spiro-OMeTAD”), a solid organic hole transport material. It has been found that the conversion efficiency exceeds 10% (Non-Patent Document 2).
This all-solid solar cell, what is called an organic-inorganic hybrid solar cell, using a perovskite-type crystal as a photoelectric conversion material has since then been developed rapidly. The conversion efficiency exceeds 20%. Most organic-inorganic hybrid solar cells reported use, as a hole transport material, spiro-OMeTAD with the following structure:

Meanwhile, inorganic materials have been applied to a hole transport layer of the organic-inorganic hybrid solar cell in some studies. Specifically, cuprous thiocyanate was employed as the hole transport material. This material, however, is toxic and is thus unsuitable as a material used for the outermost layer.    Patent Document 1: PCT International Publication No. WO2015/016107A1    Non-Patent Document 1: J. Am. Chem. Soc., 131, 6050 (2009)    Non-Patent Document 2: Science, 338, 643 (2012)    Non-Patent Document 3: J. Am. Chem. Soc. 2014, 136, 10996    Non-Patent Document 4: Chem. Commun., 2014, 50, 6931-6934